Runway 22L is far enough away from runway 13L that they can use both for simultaneous landings. I've actually seen them land THREE planes at the same time using runways 22L, 13L and 13R (usually Delta aircraft) and a few other combinations. They usually use this approach pattern between 12PM-6PM when arrival traffic is really heavy and there aren't as many departures. After 6, they just switch one runway for arrivals and one for departures, though they will mix it a bit.

And 13L/31R are the same runways, just different directions. It seems wierd that they would use use 13L for landings and 31R for departures. Come to think of it, they don't usually use 13L/31R for departures because it would take the plane residential areas. But I have seen them use both 13's (and 31's for that matter) for departures when departure traffic is really, really heavy. It looks really cool to see two 747's take off at the same time -- one turing towards the Atlantic Ocean and the other turning slightly the other way.

Yesterday they were only using the 13's for arrivals, and departures. After 2p, they also opened up 22L for some arrivals. There is no way to use both 31, and 13 at the same time. Traffic would face into each other, not good at all.

You might have misheard, or the ATIS was just incorrect that hour. Typical flow when the wind is out of the south, as it was yesterday, is 13L and 22L for arrivals, 13R for departures. 13R instead of 31R. I've never seen a flow that has 31R for departures. Not much room down there to line up planes, and 31L works a lot better for departure routes. Probably a typo.